1. Field of the Invention
The present invention relates to an electronic musical instrument for generating musical tones changing like a natural musical instrument having a decay tone property such as a plucked string instrument.
2. Description of the Related Art
In the recent years, a wide variety of musical tones have been generated from electronic musical instruments with the improvement of techniques. Various types of physical model (delay feedback algorithm) tone generators for synthesizing tones of natural musical instruments by operating models obtained through simulating the principle of tone generation of the actual natural musical instruments have been proposed as one of tone generators for use in the electronic musical instruments.
Among the physical model tone generators, a tone generator having a structure in which a nonlinear element simulating the elastic characteristic of a string and a delay circuit having a delay time equivalent to the vibration period of the string are connected in a closed loop is known as a physical model tone generator for simulating a string instrument. A signal circulating in the loop is picked up out of the loop as a tone signal of a string instrument, while the loop circuit can be deemed to life in a resonant state. This type of technique has been disclosed in Japanese Patent Unexamined Publication No. Sho-63-40199 (U.S. Pat. No. 4,984,276), Japanese Patent Postexamin. Publication No. Sho-58-58679 (U.S. Pat. No. 4,130,043), and Japanese Patent Postexamin. Publication No. Sho-58-48019.
To generate a plurality of musical tones, a plurality of tone generator channels are used and each of the tone generators has a loop circuit. For example, a rubbed string instrument such as a violin generally requires four channels and a plucked string instrument such as a guitar generally requires six channels, for corresponding with strings of the natural instruments. A driving signal generator for giving a driving signal to the loop circuit is provided in each of the channels.
For example, a driving waveform ROM is provided in each of the physical model tone generators. Accordingly, the number of driving waveform ROMs must increase by the number of tones to be generated.
Further, parameters of an LPF 12, an APF 13 and the like to give a variation to the tone signal are calculated by arithmetic operations. On the other hand, rapid response is required at the time of tone generation (or in the period of tone generation) to prevent the lagging of tone generation. Therefore, a special processor such as a high-speed CPU or a dedicated numerical operation processor is required in order to carry out the arithmetic operations at the time of tone generation or in the period of tone generation.
Further, if the aforementioned conventional electronic musical instrument, noise may be produced when parameters (such as a feedback coefficient and a filter coefficient in the closed loop) for constituent elements in each of the physical model tone generators are changed widely, because a discontinuous portion is formed in the output signal at the time of the changing of the parameters.
Further, the output signals from the respective physical model tone generators are mixed simply. Accordingly, wide performance effects of echo, chorus, etc., cannot be achieved.
Further, when a released key in a keyboard in a control manipulator is newly depressed in the condition in which the tone of the channel (physical model tone generator) assigned for the released key decays but remains, the CPU carries out a forcing damp process and then gives a tone generation starting instruction to the corresponding physical model tone generator again in the timing of the channel. Accordingly, the performance style of repeatedly manipulating a string or key in the condition in which the tone of the string or key remains as if a string in a plucked string instrument such as a guitar were repeatedly plucked cannot be simulated.